1. Field of Invention
The present invention pertains to the field of Positron Emission Tomography (PET). More particularly, this invention is directed to a device for improving the speed and accuracy of on-line three-dimensional (3D) LOR-to-bin mapping.
2. Description of the Related Art
Various techniques are used for medical imaging. Positron emission tomography (PET) is one of several popular methods in radiology because of its ability to non-invasively study physiological processes and structures within the body. PET is a nuclear imaging technique used in the medical field to assist in the diagnosis of diseases. PET allows the physician to examine the whole patient at once by producing pictures of many functions of the human body unobtainable by other imaging techniques. In this regard, PET displays images of how the body works (physiology or function) instead of simply how it looks. PET is considered the most sensitive, and exhibits the greatest quantification accuracy, of any nuclear medicine imaging instrument available at the present time. Applications requiring this sensitivity and accuracy include those in the fields of oncology, cardiology, and neurology.
In PET, short-lived positron-emitting isotopes, referred to as radiopharmaceuticals, are injected into a patient. When these radioactive drugs are administered to a patient, they distribute within the body according to the physiologic pathways associated with their stable counterparts. As the radiopharmaceutical isotopes decay in the body, they discharge positively charged particles called positrons. Upon discharge, the positrons encounter electrons, and both are annihilated. As a result of each annihilation event, gamma rays are generated in the form of a pair of diametrically opposed photons approximately 180 degrees (angular) apart. After the PET scanner detects these annihilation “event pairs” over a period of time, the isotope distribution in a cross section of the body is reconstructed. These events are mapped within the patient's body, thus allowing for the quantitative measurement of metabolic, biochemical, and functional activity in living tissue. More specifically, PET images (often in conjunction with an assumed physiologic model) are used to evaluate a variety of physiologic parameters such as glucose metabolic rate, cerebral blood flow, tissue viability, oxygen metabolism, and in vivo brain neuron activity.
In PET, it is well know that data acquisition is limited by several physical constraints of the hardware implemented. A fundamental requirement for 3-D PET is the proper positioning of each coincidence event into the 3-D projection data space. Rebinning is a positioning calculation which may use a nearest-neighbor LOR-to-projection-bin mapping. When rebinning is performed rapidly, higher patient throughput results. High-sensitivity, high-resolution PET requires that more complex rebinning calculations be performed at higher rates. These requirements place increasing demands on the data acquisition electronics.
The pursuit of greater sensitivity in 3-D PET typically leads to ever-larger detector arrays and higher count rates. Preserving good image resolution in larger detector arrays requires more complex calculations. In the present case, more calculations are required for properly positioning coincidence LORs into the 3-D projection data space. As a result of this progression, algorithms and electronic architectures which were once adequate for the smaller, shorter-axis detector arrays are no longer adequate. As the axial extent of the detector array increases, the data acquired from conventional algorithms degrades. Accordingly, algorithms and electronic architectures required to service on-line rebinning for larger, longer-axis PET detector arrays must be improved, especially where image resolution is critical. One example of a long-axis high-resolution PET is described by Wienhard et al., “The ECAT HRRT: Performance and First Clinical Application of the New High Resolution Research Tomograph,” IEEE Trans. Nucl. Sci., vol. 49, pp. 104-110 (2002). With an eye toward the clinical needs of high patient throughput, challenges to the on-line electronics include more complex rebinning algorithms and higher rebinning rates.
In earlier work on digital pipelines for on-line PET rebinning, flash memory chips used as look-up tables (LUT) were applied in various pipeline stages using programmable logic. See, for example, W. Jones, et al., “LSO PET/SPECT Spatial Resolution: Critical On-line DOI Rebinning Methods and Results,” IEEE MIC Conf. Rec., (2000); and W. Jones, et al., “First Time Measurement of Transaxial Resolution for a New High-Sensitivity PET Prototype Using 5 LSO Panel Detectors,” IEEE MIC Conf. Rec., (2002).